This invention relates to ink jet printers and particularly to those having a plurality or multiplicity of ink jet heads in alignment for printing as many characters or symbols on a continuous strip of paper or like printable material traveling along a predefined path.
One of the essentials for production of high quality printings by ink jet printers of the kind under consideration is that there be an unvarying spacing between the series of ink jet heads and the surface of the strip of paper to be printed. Typical of contrivances heretofore made to attain this objective are those described and claimed by Japanese Unexamined Patents Publication Nos. 5-124284 and 6-199457. They are alike in teaching a single ink jet head or pen printer wherein a continuous web or individual sheets of paper or the like are printed upon while traveling on a fixed, flat platen, by which is held constant the spacing between head and paper.
The fixed flat platen has proved unsatisfactory, however, when incorporated in multiple head ink jet printers in which a multiplicity of ink jet heads are aligned along a predefined path of a continuous strip of paper or like printable material for printing as many characters or symbols thereon. Consider an elongate flat platen mounted opposite to the series of ink jet heads, and with the paper strip fed over the platen by guide rollers or pairs of feed rollers disposed adjacent to both ends of the platen. The paper strip has been very easy to flutter over the platen by reason of the inconveniently long distance between the guide rollers or the like, thereby giving rise to variations in the spacing between the paper strips surface and the heads.
Such inconveniences have become even more pronounced in printers using an aqueous ink. Almost unavoidably stretched out, slackened, or creased by the ink moisture, the paper strip has often failed to travel at a desired constant distance from the ink jet heads, no matter how much it is tensioned as by increased feeding force or braking.
The Japanese unexamined patent publications cited above employ means in addition to the flat platen for holding the paper against it. However, such means are effective only in single-head printers, not applicable to multiple head devices where the paper must travel stably a much longer distance past a row or rows of multiple heads.